This invention relates to the controlled fracturing and loosening of geological formations, such as those surrounding the bore hole of a well, as frequently done to initiate or to improve petroleum production from a drilled formation, an operation known in the art as "shooting" the well, and the function of which is to provide an escape path to the bore hole for bodies of petroleum which are entrapped in the geological formation.
Heretofore, oil wells have been "shot" with nitroglycerine, which must be transported from the site of use. Such transportation is hazardous, not only to the occupants of the vehicle which transports the nitroglycerine but also to the other users of the roads, highways and fields over which such transportation must take place. More over, the handling of nitroglycerine at the site of use, as well as the onsite operations of charging containers (so called "torpedoes") with it, emplacing the torpedos at the proper elevation in the bore hole (more often than not under water), and finally setting and emplacing at least one "time bomb" to detonate the nitroglycerine charges, involve a greater degree of hazard, albeit to fewer people, than does the transportation thereof to the well site. Despite the exceptionally high degree to care exercised by skilled well shooters, more than a few of them have lost their lives or limbs, or have been maimed for life in the course of such operations.
It is therefore the object of the present invention to minimize the hazard involved in shooting wells, providing means for providing on-site assembly of various components that are useful for enhancing petroleum production from a well, and which can be handled relatively free of any hazard which, as previously described, is always present when operating with nitroglycerine charges, or the like.
For some years, many skilled oil well shooters have recognized that the shock waves generated by the detonation of nitroglycerine with a well are not ideal for the purpose intended. There are two schools of thought -- frequently over-lapping on the subject. One school holds that the shock waves generated by nitroglycerine have a frequency too high for optimum results. The other school holds that the duration (life to decay) of shock waves generated by nitroglycerine is too short for optimum results. Most experienced shooters appear to agree, however, that it is virtually impossible to accomplish with nitroglycerine an effective shot while the bore hole is occupied, at least at the shooting elevation, with acid put there in the course of an unsuccessful acidizing treatment; and that too often a nitroglycerine shot collapses open-ended tubing in the well.
Accordingly, it is another object of the invention to obviate the aforesaid objections to shooting wells with nitorglycerine.
These and other objects of the invention are achieved by the utilization of the reaction of an Alkali metal (sodium, potassium, cesium, rubidium, lithium) with water as the source of energy for shooting wells, and which charges can be prepared for immediate use at the site of the well.
The invention evolved from experience with an oil well about 3,200 feet deep which had previously been a fair producer of oil and a good producer of gas, but whose production of gas had declined to near zero, and whose oil production had declined to about one barrel per day. The well had been shot with nitorglycerine and had been acidized, without noticeable improvement in production. The well was filled with liquid to the level of about 2,500 feet below ground, and was about to be abandoned when, at my suggestion, three pounds of sodium (in two oil coated pieces) were dropped into it. Production of copious natural gas was resumed immediately, and the production of oil increased to about 69 barrels per day.
Unlike nitroglycerine, and other "high" explosives, the Alkali metals do not detonate when subjected to impact, heat or flame; but do detonate upon contact with water (usually present in more or less degree in any oil well to be shot) or with acid (frequently present). Such detonation is attended by the release of a mol of hydrogen for each mol of water that reacts with a mol of the Alkali metal to produce the hydroxide of the metal, and thereby release a quantum of energy equal to the heat generated by the exothermic reaction. For instance, with sodium, which is the most readily and economically available of the Alkali metals, the reaction with water occurs, albeit at a rate less than detonation, when the metal is exposed to atmospheric humidity, but the customary preventative is to handle and transport sodium in a blanket of nitrogen or other non-reactive gas such as argon or helium, or to coat it with oil or grease.
The hydrogen released by the reaction of sodium with water or acid, if in the presence of air or other available oxygen, will, if ignited, produce more water; and if so ignited in contact with carbonaceous material, such as petroleum, will produce carbon dioxide. Carbon dioxide dissolved or entrained in water constitutes a composition which has been reported to increase more than a hundred times, the solubility of such calcerious materials as argonite and calcite over their solubility in cold water at about forty times their solubility in hot water; and if sulphuric acid is present, or the petroleum is sulfurous, as when produced from calcerious formations containing anhydrite or gypsum, the concurrent reactions may yield hyposulfite, which is a well-known solvent for anhydrite and gypsum. Consequently, when sodium is employed as the explosive to loosen oil-bearing calcerious formations, there is an inherent advantage of providing, in situ, a secondary result of the same kind as, albeit lesser in degree than, that achieved by conventional acidizing of wells. However, aside from safety, the major operating advantage of shooting wells with sodium or other Alkali metals is attributable to the character and duration of the shock waves which emanate from their reaction with water.
The shock waves which emanate from the reaction of sodium with water appear, from surface sensation, to have a substantially lesser frequency than those produced by the detonation of nitroglycerine; and the duration of the wave action appears to be about 50 times as long as those produced by the detonation of nitroglycerine. This difference in the character and duration of the shock waves appears to have a markedly different effect on the geological formation being shot. Nitroglycerine tends to locally shatter the formation, whereas the sodium-water reaction appears to loosen it over a much greater radius. These contrasting effects may be attributable to the fact that an entire charge of nitroglycerine detonates instantaneously, whereas the reaction between sodium and water, depending, as it does, upon the magnitude of the area of the sodium charge exposed at any increment of time to the water, is more time-consuming and more readily controlled by varying the surface area of a body of metallic sodium which will be exposed to water.